Photochromic spectacles are the spectacles which, when irradiated with light containing ultraviolet rays such as of sunlight as in the outdoors, quickly develop color in the lenses thereof to work as sunglasses and, in the indoors where there is no irradiation of such light, fade color to work as ordinary transparent spectacles. In recent years, the photochromic spectacles having such features have been demanded more than ever before.
As the photochromic spectacle lenses, in particular, the plastic lenses imparted with photochromic properties have been widely used from the standpoint of small weight and safety. To impart the plastic lenses with photochromic properties, in general, an organic photochromic compound is used; i.e., the photochromic properties are imparted to the plastic lenses by a method called imbibition method or in-mass method.
The imbibition method is a method of expressing photochromic properties by having a photochromic compound imbibed in the surfaces of the plastic lenses.
The in-mass method is a method of directly obtaining lenses having photochromic properties by dissolving a photochromic compound in a polymerizable monomer which is, thereafter, polymerized.
In addition to the above methods, there has, further, been known a method called coating method.
In the coating method, a coating agent (photochromic coating agent) containing a photochromic compound is applied on the surfaces of the plastic lenses and is cured to form a coating (photochromic coating) having photochromic properties.
However, it is not easy to realize the photochromic properties required for the photochromic spectacle lenses relying only upon the thin photochromic coating. At present, therefore, many of the photochromic lenses that are practically used have been produced by the imbibition method or by the in-mass method.
In recent years, however, a photochromic coating agent has been developed by which the photochromic properties can be realized even in the form of a thin photochromic coating, and expectations for the coating method are now sharply increasing.
The advantage of the coating method is that it is, in principle, capable of easily imparting photochromic properties to any lens materials. In the imbibition method, for example, the lens material must be a soft material so that the photochromic compound can be easily dispersed therein. In the in-mass method, too, the lens material (photochromic lenses) must be produced by using a special monomer to express good photochromic properties. The coating method, however, has no such limitations on the lens materials.
Described below are representative photochromic coating agents (a) to (d) that have been proposed to be applied to the spectacle lenses.    (a) A photochromic coating agent comprising an urethane oligomer in which a photochromic compound is dissolved (see a patent document 1).    (b) A photochromic coating agent comprising a polymerizable monomer having a (meth)acrylic group, a polymerizable monomer having two (meth)acrylic groups and a polymerizable monomer having three or more (meth)acrylic groups in combination at a specific ratio and in which a photochromic compound is dissolved (see a patent document 2).    (c) A photochromic coating agent comprising a plurality of kinds of polymerizable monomer components only selected from the polymerizable monomers having two (meth)acrylic) acrylic groups, and in which a photochromic compound is dissolved (see a patent document 3).    (d) A photochromic coating agent comprising a curable composition containing a photochromic compound, an amine compound, a radically polymerizable monomer having a silanol group and/or a radically polymerizable monomer having an isocyanate group (see a patent document 4).
As a coating agent used for the production of optical recording devices, further, there has been proposed the (e) coating agent comprising a solution of a silsesquioxane having a (meth) acrylic group, a poly (meth) acrylate, a photo sensitizer and a radical polymerization initiator, in which a photochromic compound is dissolved or dispersed (see a patent document 5).
In the use of spectacle lenses, on the other hand, it can be contrived to use the photochromic curable composition (i.e., curable composition used for forming lenses) used in the in-mass method as the photochromic coating agent.
As the photochromic curable composition used in the in-mass method, there has been known, for example, (f) a curable composition that contains a polyurethane prepolymer, a silsesquioxane and a photochromic compound (see a patent document 6).
However, the photochromic coatings formed by using the above photochromic coating agents (a) to (d) have low scratch resistance, and tend to be easily scratched in the step of working the lenses, such as in the step of polishing the back surfaces of the lenses for attaining desired degrees or in the step of chamfering the outer circumferential portions to meet the shape of the frames. That is, to obtain good properties of the photochromic spectacle lenses, i.e., to obtain a high color density and a high fading rate, the photochromic coating must be formed soft resulting, however, in a decrease in the scratch resistance.
The above coating agent (e) is suited for the use with the optical recording devices and is blended with the photochromic compound without, however, paying attention to the properties related to reversible color changes (i.e., photochromic properties). Besides, according to the study by the present inventors, it was found that the film formed by using the above coating agent cannot exhibit photochromic properties to a sufficient degree. Specifically, when there is used a compound having an indeno[2,1-f]naphtho[1,2-b]pyran skeleton that exhibits excellent properties as a photochromic compound, the photochromic properties are not almost exhibited.
The above curable composition (f) makes it possible to obtain a cured body having good scratch resistance but is highly viscous and is not suited for use as the photochromic coating agent. Further, if the photochromic lenses are formed by the in-mass method by using the above curable resin, the lenses that are obtained fail to exhibit satisfactory photochromic properties from the standpoint of, specifically, fading rate.
A patent document 7 discloses a coating comprising a polysilsesquioxane-containing polymer which excels in scratch resistance and closely adheres to an antireflection film or the like film when it is placed under an oxidizing condition without, however, quite giving attention to the photochromic property when the coating is blended with a photochromic compound.